A common method of growing oysters is to place them in cages that are suspended under floats, thereby positioning the growing oyster close to the surface of the water where optimal growing conditions exist. This method protects the oysters from predation and keeps them well above the seabed reducing the amount of suspended sediments in the water being taken up by the filter-feeding oysters and increasing the amount of plankton and other nutrients available to the oysters. Positioning the oysters close to the surface also tends to increase the water flow passing through the culture cage as well as the water temperature, both factors increasing oyster growth rates and therefore reducing the time required to bring an oyster to market size.
Regardless of the position of the culture cage in the water column, the accumulation of biofouling on the cage and on the oysters themselves can reduce water flow, increase the drag of the cage, and result in oysters that require more cleaning after they are harvested. Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or animals on wetted surfaces. However, if the culture cage is suspended under a float or floats of sufficient size, the cage and float assembly can be inverted, positioning the cage and the oysters inside the cage out of the water and subjecting them to drying from the action of sun and wind. This drying tends to kill the fouling organisms but has little effect on the oysters, a species that is able to tolerate the process.
By controlling the amount of time the cage is inverted, the biofouling can be reduced or eliminated and the health and growth rate of the oysters can be improved. Typically, an oyster cage is inverted for one day and then returned to its normal position the day after. Twenty-four hours of exposure to air-drying seems to be sufficient to kill most fouling organisms. Typically, this process, called flipping, must be done about every two weeks to be effective. The timing of this flipping will vary with oyster farm location, time of year, weather, water temperature, and knowledge of the local presence of fouling organisms.
This flipping process is generally labor intensive, being done manually by crew working from boats. The cages, particularly when they are full of mature oysters are heavy and often require two strong persons to lift one side of the cage, rotate it, and ensure the cage ends up in the desired position. A common means of doing this it to have a submerged work platform suspended over the side of a boat, resulting in the cage being at a convenient height with respect to the arms of the flipping crew.